Targeting tumours. Computer artwork of a malignant (cancerous) tumour with a target over it. This could represent the more specific targeting of cancer cells by drugs. Chemotherapy and radiotherapy affect all the cells in the body, although they do have a greater affect on cancer cells, and so produce many undesired side effects. Drugs that are targeted only at cancerous cells are often more efficient (as they are needed in smaller doses) and do not have as many deleterious systemic side effects.